Outdoor navigation and positioning has been widely deployed following the development of various global navigation-satellite-systems (GNSS) as well as various cellular systems. Indoor navigation and positioning differs from outdoor navigation and positioning because the indoor environment does not enable the reception of location signals from satellites or cellular base stations as accurately as in the outdoor environment. As a result, accurate and real-time indoor navigation and positioning are difficult to achieve. Solutions for indoor navigation and positioning involve time-of-flight (ToF) positioning protocols.
When using the ToF protocols for indoor positioning, link adaptation is unwanted because the client may be moving, causing rapid channel changes. Additionally, the ToF protocol might be conducted in un-associated mode. The most robust modulation protocols use lower modulation and coding schemes (MCS), and because the packets are relatively short, the coding penalty is small. When transmitting in a lower MCS, the 802.11 standard permits a higher error vector magnitude (EVM) because a higher EVM enables transmitting at higher power. Unfortunately, transmitting at the higher power drives the power amplifier (PA) to operate in a non-linear range. Although high power transmission increases Wi-Fi coverage without affecting the bit error rate, it degrades the performance of the ToF ranging measurements because the measurement quality is directly related to channel quality estimation. In certain scenarios, especially non line of sight (NLoS) scenarios, the EVM of the channel estimation is crucial.
Thus, there is a need for accurate indoor ToF navigation and positioning apparatus and methods. There are also general needs for ToF navigation and positioning apparatus and methods that optimally control transmit EVM power according to client conditions.